Bharat Ratra (Kansas State U.) "Dark Energy: Constant or Time Variable? (…and other open questions)""

Experiments and observations over the last two decades have persuaded cosmologists that (as yet undetected) dark energy is by far the main component of the energy budget of the universe. I review a few simple dark energy models and compare their predictions to observational data, to derive dark energy model-parameter constraints and to test consistency of different data sets. I conclude with a list of open cosmological questions.